2024 Yılı YTMK Geleneksel Ödül Yarışması’nda Emre Tekdemir ve Erman Ergincan’ın tezlerine yılın tezi ödülü

2024 Yılı YTMK Geleneksel Ödül Yarışması’nda Boğaziçi Üniversitesi’ne iki ödül birden:

2024 Yılı YTMK Geleneksel Ödül Yarışması’nda yılın yüksek lisans tezi dalında Emre Tekdemir’in ve Erman Ergincan’ın, Zeynep Yıldırım danışmanlığında 2023-2024 döneminde tamamlanan tezleri ödül aldı.

Ödülle ilgili habere aşağıdaki linkten ulaşabilirsiniz:
https://www.ytmk.org.tr/duyurular/yollar-turk-milli-komitesi-2024-yili-y...

Her iki öğrencinin de tez çalışması İrem Zeynep Yıldırım’ın Start-Up BAP Projesi SUP 16961 kaynaklarıyla desteklenmiştir ve tezlerinde bu projeye atıf vardır.

1. Yılmaz Emre TEKDEMİR’in “Kazıklarla stabilize edilmiş killi şevlerin üç boyutlu kısa dönem stabilite analizi” (Three-dimensional short-term stability analysis of clayey slopes stabilized with piles) konulu Yüksek Lisans Tezi, Boğaziçi Ün. Danışman:  İrem Zeynep Yıldırım

Abstract:
In this study, the short-term (undrained) behavior of pile-stabilized clayey slopes were investigated via three-dimensional (3D) finite element analysis. Deformations and stability conditions were investigated considering various soil strength parameters, slope geometries, pile material behavior, pile head conditions, and pile spacing-to-diameter ratios for slopes with and without surcharge loads. For the slopes without surcharge loads, the slopes were modeled as a representative slice model and the loaded slopes were modeled using the complete geometry of the problem to capture the 3D failure mechanism induced by the local surcharge loads. Initial case selection was performed using limit-equilibrium based slope stability analysis and based on the initial factor of safety values, slopes that were deemed feasible to be stabilized with piles were selected for the parametric study. Factor of safety values, internal pile forces, pile head displacements, and failure mechanisms were recorded and used to evaluate the performance of various pile-stabilized slope cases. The results indicate that using elasto-plastic pile models improves the accuracy of the analysis by better simulating pile behavior and coupled failure mechanisms, resulting in more reliable factor of safety values. The effectiveness of soil arching and pile stabilization decrease as the pile spacing-to-diameter ratios and slope heights increase. In cases of high and steep, natural slopes (slope height, H≥25m, slope angle, β≥56.3°), and high and gentle, loaded slopes (slope height, H≥15m, slope angle, β≤33.7°), marginal improvements were observed through stabilization by a single row of piles. For other slope geometries, pile stabilization performed reasonably well. When the factor of safety of a slope reduces below 1 due to surcharge loads, significant deformations occur, and stabilizing the slope with piles becomes an inefficient solution. In locally loaded slopes, central piles experience severe loading, leading to structural failure and subsequent slope failure. The employment of a pile cap to constrain pile head movements improves stability by ensuring an even load distribution among row of piles. The results highlighted the importance of 3D analysis when pile stabilized slopes are considered.

2. Hakkı Erman ERGİNCAN’ın  “Boru kemer yöntemiyle desteklenen NATM tünellerin sayısal modellemesi ve parametrik çalışması”  (Numerical modeling and parametric study of NATM tunnels supported by umbrella arch)  konulu Yüksek Lisans Tezi, Boğaziçi Ün., Danışman: İrem Zeynep Yıldırım Eş Danışman: Tolga Özüdoğru

Abstract:
In this numeric study, the behaviors of tunnels supported by the umbrella arch method were investigated parametrically through two-dimensional (2D) finite element models. Firstly, the numerical modeling concept was validated principally by comparing the results of the models with the real measurements taken from two different twin tunnel sections excavated with the New Austrian Tunnel Method (NATM) and supported by the umbrella arch (UA) located in the Çekmeköy-Sancaktepe-Sultanbeyli Metro Line project. For the validation, the models were created with three different approaches called plate (P), dummy plate (DP), and individual pipe (IP) in the literature, and their appropriateness was evaluated. All three approaches succeeded in predicting the surface settlement with an acceptable error margin. In comparison with the two others, DP approach predicted the real site data more precisely, and it was adopted to proceed with the parametric studies. Based on the validation study, by using constant deconfinement ratios, a total of 162 models were created for the parametric study with and without UA as a combination of three tunnel diameters, three overburden depths, three clear distance ratios between twin tunnels, and three soil conditions. These models were analyzed comparatively in terms of forces and displacements. The results indicated that maximum vertical displacement governs the maximum resultant displacement in tunnels, and surface volume loss (VS) increases as inner tunnel volume loss (VL) increases, and VL increases as ground conditions worsen. Their ratio (VS/ VL) decreased with the reduction in tunnel diameter (D) or overburden depth (C). The results showed that the twin tunnels converge differently due to geometry and ground conditions, and this difference causes asymmetric settlement profiles, which may also include two peaks as the distance between tunnels increases and C/D decreases. In the aspect of forces on support elements, the factor of safety increases as tunnel diameter gets smaller, overburden depth gets shallower, clear distance gets larger, and ground condition gets better. The results implied the importance of deconfinement ratio to simulate UA effect in 2D.